1. Field of the Invention
This invention relates to touch sensors, in particular to acoustic touch sensors and acoustic touchscreens having narrow functional borders and increased touch-sensitive areas.
2. Introduction to the Invention
An acoustic touch sensor has a touch sensitive area on which the presence and location of a touch is sensed by the touch's effect on the transmission of acoustic waves across a touch sensor substrate. Acoustic touch sensors may employ Rayleigh waves (including quasi-Rayleigh waves), Lamb or shear waves, or a combination of different types of the acoustic waves.
FIG. 1 illustrates the operation of a conventional acoustic touch sensor, an acoustic touchscreen 1. The touchscreen 1 has a touch-sensitive area 2 inside of which two-dimensional coordinates of touches are determined. For example, the touch-sensitive area 2 may include the region bounded by the dashed line 16 which represents the inner boundary of a bezel 10. A first transmitting transducer 3a is positioned outside of touch-sensitive area 2 and is acoustically coupled to the surface of touchscreen 1. The transducer 3a sends an acoustic signal in the form of an acoustic wave 11a traveling parallel to the top edge of touchscreen 1 and generally in the plane of touchscreen 1. Aligned in the transmission path of acoustic wave 11a is a first linear array 13a of partially acoustically reflective elements 4, each of which partially transmits the acoustic signals and partially reflects them (by an angle of approximately 90°), creating a plurality of acoustic waves (e.g., 5a, 5b and 5c) traveling vertically across touch-sensitive area 2. The spacing of reflective elements 4 is variable to compensate for the attenuation of the acoustic signals with increasing distance from first transmitter 3a. It is also well known even if reflective elements 4 are uniformly spaced, signal equalization may be achieved by varying the reflective strength of reflective elements 4. Acoustic waves 5a, 5b, and 5c are again reflected by an angle of approximately 90° (see arrow 11b) by a second linear array 13b of partially acoustically reflective elements 4 towards a first receiving transducer 6a upon reaching the lower edge of touchscreen 1. At the receiving transducer 6a, the waves are detected and converted to electrical signals for data processing. Similar arrangements of reflective elements are located along the left and right edges of touchscreen 1. A second transmitting transducer 3b generates an acoustic wave 12a along the left edge, and a third linear array 13c of partially acoustically reflective elements 4 creates a plurality of acoustic waves (e.g., 7a, 7b, and 7c) traveling horizontally across touch-sensitive area 2. Acoustic waves 7a, 7b, and 7c are redirected along 12b by a fourth linear array 13d of partially acoustically reflective elements 4 towards receiving transducer 6b, where they are detected and converted to electrical signals for data processing.
If touch-sensitive area 2 is touched at position 8 by an object such as a finger or stylus, a portion of the energy of the acoustic waves 5b and 7a is absorbed by the touching object. The resulting attenuation is detected by receiving transducers 6a and 6b as a perturbation in the acoustic signal. A time delay analysis of the data with the aid of a microprocessor (not shown) allows determination of the coordinates of touch position 8. The device of FIG. 1 can also function as a touchscreen with only two transducers using a transmit/receive transducer scheme.
A housing 9, indicated by dashed lines in FIG. 1, may be associated with touchscreen 1. The housing can be made of any suitable material, for example molded polymer or sheet metal. The housing 9 includes a bezel 10, indicated by dashed line 16 representing an inner boundary of bezel 10 and dashed line 17 indicating an outer boundary of bezel 10 in FIG. 1. The inner dashed line 16 shows that the housing 9 overlays a periphery of touchscreen 1, concealing the transmitting and receiving transducers, the reflective elements, and other components, but exposing touch-sensitive area 2. This arrangement can protect the concealed components from contamination and/or damage, provide an aesthetic appearance, and define the touch-sensitive area for the user.
A touchscreen may comprise a separate faceplate overlaid on a display panel. The faceplate is typically made of glass, but any other suitable substrate may be used. The display panel may be a cathode ray tube (CRT), a liquid crystal display (LCD), plasma, electroluminescent, organic light-emitting-diode (OLED) display, or any other type of display.
As shown in FIG. 1, the touch sensitive area 2 is surrounded by border regions 15 where the reflective elements 4 and the transmitting and receiving transducers 3a, 3b, 6a and 6b are located. Reducing the width of border regions 15 increases the touch sensitive area 2. For touch sensor applications using transparent touch sensors such as touchscreens, the width of the border can be especially important. A touch sensor with narrowed border regions 15 can be integrated into display monitors that themselves have a narrow border around the displayed image. This feature is desirable as the general market trend for devices such as monitors is towards sleeker and more mechanically compact designs. A touch sensor with narrowed border regions 15 also is more easily sealed as well as being lighter and can have increased sensor area. Amongst competing touchscreen technologies, (e.g., acoustic, capacitive, resistive and infrared) acoustic touchscreens tend to have wider borders.
It is possible to reduce the border region of a touchscreen by using a waveguide to concentrate an acoustic wave in the border region, as disclosed in U.S. Pat. No. 6,636,201, the disclosure of which is incorporated herein by reference. However, alternate solutions may be desired which do not require providing a waveguide on the touch surface of the touch sensor substrate.
For the reasons outlined above, it is desirable to have acoustic touch sensor designs capable of accommodating a very narrow border region.